ClassFlow is a free program where you can upload Promethean Board Flipcharts and each student can get that flipchart on their iPad. I uploaded word sorts so I can easily switch the sort for each group.
This is what it looks like on my laptop but you can also do it right from your Promethean board.
When you stop the session you can see each students flipchart on your teacher screen. I think the Teacher App lets you do it from another iPad.